The Common Lisp Cookbook – Using Emacs as an IDE

Table of Contents

The Common Lisp Cookbook – Using Emacs as an IDE

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This page is meant to provide an introduction to using Emacs as a Lisp IDE.

We divided it roughly into 2 sections: how to use Slime or Sly, and complementary information on built-in Emacs commands to work with Lisp code.

We want to bring Portacle to your attention. It is a portable and multi-platform CL development environment shipping Emacs, Slime, SBCL, git and necessary extensions. It is a straightforward way to get going.

Why Use Emacs?

SLIME: Superior Lisp Interaction Mode for Emacs

SLIME is the goto major mode for CL programming. It has a lot of features that make it a powerful, integrated and very interactive development environment.

SLY: Sylvester the Cat’s Common Lisp IDE

SLY is a SLIME fork that contains the following improvements:

Sly is shipped by default in Doom Emacs.

Installing SLIME or SLY


On Ubuntu, SLIME is easily installed alongside Emacs and SBCL:

sudo apt install emacs slime sbcl

Otherwise, install SLIME by adding this code to your ~/.emacs.d/init.el file:

(require 'package)
(add-to-list 'package-archives '("melpa" . "") t)
(dolist (package '(slime))
  (unless (package-installed-p package)
    (package-install package)))
(require 'slime)

assuming you’ve also instealled Emacs and SBCL.

Since SLIME is heavily modular and the defaults only do the bare minimum (not even the SLIME REPL), you might want to enable more features with

(require 'slime)
(slime-setup '(slime-fancy slime-quicklisp slime-asdf slime-mrepl))

After this you can press Alt-X on your keyboard and type slime and try Common Lisp!

(Alt-X is often written M-x in Emacs-world.)

For more details, consult the documentation (also available as an Info page).

Now you can run SLIME with, as mentioned, M-x slime and/or M-x slime-connect.

See also:


Portacle is a portable and multi-platform CL development environment with which you can start developping in Lisp in a few clicks. Portacle includes Emacs, SBCL, Slime, git, and useful Emacs extensions (which-key, treeview…).

It is a straightforward way to get going.

Doom Emacs

Doom Emacs is a popular Emacs configuration. You can easily enable its Sly integration.

SLIME fancy and contrib packages

SLIME’s functionalities live in packages and so-called contrib modules must be loaded to add further functionalities. The afored mentioned slime-fancy includes:

SLIME also has some nice extensions like Helm-SLIME which features, among others:

Working with SLIME (or SLY)

One of the first things you might want to do is to compile and load some Lisp code. Use C-c C-c on a function or C-c C-k to compile a whole file. But that’s not all, read on.

Note that we give function names for SLIME. They are most of the time similar with SLY.

Code completion

Use the built-in C-c TAB to complete symbols in SLIME. You can get tooltips with company-mode.

In the REPL, it’s simply TAB.

Use Emacs’ hippie-expand, bound to M-/, to complete any string present in other open buffers.

Evaluating and Compiling Lisp in SLIME

Compile the entire buffer by pressing C-c C-k (slime-compile-and-load-file).

Compile a region with M-x slime-compile-region.

Compile a defun by putting the cursor inside it and pressing C-c C-c (slime-compile-defun).

Once you compiled some code, you can try it, for example on the REPL.

To evaluate rather than compile:

See also other commands in the menu.

But what’s the difference between evaluating and compiling some code?

evaluation VS compilation

There are a couple of pragmatic differences when choosing between compiling or evaluating. In general, it is better to compile top-level forms, for two reasons:

eval is still useful to observe results from individual non top-level forms. For example, say you have this function:

(defun foo ()
  (let ((f (open "/home/mariano/test.lisp")))

Go to the end of the OPEN expression and evaluate it (C-x C-e), to observe the result:

=> #<SB-SYS:FD-STREAM for "file /mnt/e6b00b8f-9dad-4bf4-bd40-34b1e6d31f0a/home/marian/test.lisp" {1003AAAB53}>

Or on this example, with the cursor on the last parentheses, press C-x C-e to evaluate the let:

(let ((n 20))
  (loop for i from 0 below n
     do (print i)))

You should see numbers printed in the REPL.

See also eval-in-repl to send any form to the repl.


We cover debugging commands in its own debugging chapter.

Go to definition

Put the cursor on any symbol and press M-. (slime-edit-definition) to go to its definition. Press M-, to come back.

Go to any symbol, list symbols in current source

Use C-u M-. (slime-edit-definition with a prefix argument, also available as M-- M-.) to autocomplete the symbol and navigate to it.

This command always asks for a symbol even if the cursor is on one. It works with any loaded definition. Here’s a little demonstration video.

You can think of it as a imenu completion that always work for any Lisp symbol. Add in Slime’s fuzzy completion for maximum powerness!

Argument lists

When you put the cursor on a function, SLIME will show its signature in the minibuffer.

If you want to see them better, try C-c C-s after a function name.

For example, you forgot how to use with-open-file. Write it:


now press C-c C-s (slime-complete-form) and you’ll get:

(with-open-file (stream filespec :direction direction
                                 :element-type element-type
                                 :if-exists if-exists
                                 :if-does-not-exist if-does-not-exist
                                 :external-format external-format
                                 :class class

written in your source file (or in the REPL).

The minibuffer will show you the default values of the arguments.

Documentation lookup

The main shortcut to know is:

Other bindings which may be useful:

You can enhance the help buffer with the Slime extension slime-doc-contribs. It will show more information in a nice looking buffer, and it will add choices to the documentation command:


You can call (inspect 'symbol) from the REPL or call it with C-c I from a source file.

Learn to use with its documentation: use l to come back to the previous object, * to copy the object at point… and more.


Use C-c M-m to macroexpand a macro call

Crossreferencing: find who’s calling, referencing, setting a symbol

Slime has nice cross-referencing facilities. For example, you can ask what calls a particular function, what expands a macro, or where a global variable is being used.

Results are presented in a new buffer, listing the places which reference a particular entity. From there, we can press Enter to go to the corresponding source line, or more interestingly we can recompile the place at point by pressing C-c C-c on that line. Likewise, C-c C-k will recompile all the references. This is useful when modifying macros, inline functions, or constants.

The bindings are the following (they are also shown in Slime’s menu):

And when the slime-asdf contrib is enabled, C-c C-w d (slime-who-depends-on) lists dependent ASDF systems

And a general binding: M-? or M-_ (slime-edit-uses) combines all of the above, it lists every kind of references.

Systems interactions

In Slime, you can use the usual C-c C-k in an .asd file to compile and load it, then ql:quickload (or asdf:load-system) to effectively load the system. SLIME offers more interactive commands to interact with Lisp systems:

Sly users have a more featureful sly-load-system command that will search the .asd file on the current directory and in parent directories.

REPL interactions

From the SLIME REPL, press , to prompt for commands. There is completion over the available systems and packages. Examples:

and many more. Usually the interactive commands given in the previous section have a REPL shortcut.

With the slime-quicklisp contrib, we can use ,ql to autocomplete a system to install, from all systems available for installation.

In addition, we can use the Quicklisp-systems Slime extension to search, browse and load Quicklisp systems from Emacs.

Sending code to the REPL

You can write code in the REPL, but you can also interact with code directly from the source file.

We saw C-c C-j, that sends the expression at point to the REPL and evaluates it.

C-c C-y (slime-call-defun): send code to the REPL.

When the point is inside a defun and C-c C-y is pressed (below I’ll use [] as an indication where the cursor is)

(defun foo ()

then (foo []) will be inserted into the REPL, so that you can write additional arguments and run it.

If foo was in a different package than the package of the REPL, (package:foo ) or (package::foo ) will be inserted.

This feature is very useful for testing a function you just wrote.

That works not only for a defun, but also for defgeneric, defmethod, defmacro, and define-compiler-macro in the same fashion as for defun.

For defvar, defparameter, defconstant: [] *foo* will be inserted (the cursor is positioned before the symbol so that you can easily wrap it into a function call).

For defclass: (make-instance ‘class-name ).

Inserting calls to frames in the debugger

C-y in SLDB on a frame will insert a call to that frame into the REPL, e.g.,

(/ 0) =>

C-y will insert (CCL::INTEGER-/-INTEGER 1 0).

(thanks to Slime tips)

Synchronizing packages

C-c ~ (slime-sync-package-and-default-directory): When run in a buffer with a lisp file it will change the current package of the REPL to the package of that file and also set the current directory of the REPL to the parent directory of the file.

Exporting symbols

Slime provides a shortcut to add export declarations to your package, effectively exporting one or many symbol(s), or on the contrary un-exporting it.

C-c x (slime-export-symbol-at-point) from the slime-package-fu contrib: takes the symbol at point and modifies the :export clause of the corresponding defpackage form. It also exports the symbol. When called with a negative argument (C-u C-c x) it will remove the symbol from :export and unexport it.

M-x slime-export-class does the same but with symbols defined by a structure or a class, like accessors, constructors, and so on. It works on structures only on SBCL and Clozure CL so far. Classes should work everywhere with MOP.


There are different styles of how symbols are presented in defpackage, the default is to use uninterned symbols (#:foo). This can be changed:

to use keywords, add this to your Emacs init file:

(setq slime-export-symbol-representation-function
      (lambda (n) (format ":%s" n)))

or strings:

(setq slime-export-symbol-representation-function
 (lambda (n) (format "\"%s\"" (upcase n))))

(optional) Consult the Hyper Spec (CLHS) offline

The Common Lisp Hyper Spec is the official online version of the ANSI Common Lisp standard. We can start browsing it from starting points: a shortened table of contents of highlights, a symbols index, a glossary, a master index.

Since January of 2023, we have the Common Lisp Community Spec:, a new web rendering of the specification. It is a more modern rendering:

If you want other tools to do a quick look-up of symbols on the CLHS, since the official website doesn’t have a search bar, you can use:

We can browse the CLHS offline with Dash on MacOS, Zeal on GNU/Linux and Velocity on Windows.

But we can also browse it offline from Emacs. We have to install a CL package and to configure the Emacs side with one command:

(ql:quickload "clhs")

Then add this to your Emacs configuration:

(load "~/quicklisp/clhs-use-local.el" 'noerror)

Now, you can use C-c C-d h to look-up the symbol at point in the HyperSpec. This will open your browser, but look at its URL starting with “file://home/”: it opens a local file.

Other commands are available:

Working with Emacs

In this section we’ll learn the most useful Emacs commands to work with Lisp code in general, or to perform common actions.

We’ll start by how to find your way into Emacs’ built-in documentation. If there is a skill you should learn, that is the one.

Don’t forget that Emacs both GUI and terminal interfaces have menus, they help in discovering all available commands. If you don’t see one, ensure that your emacs configuration doesn’t hide it. Display the menu with M-x menu-bar-mode.

Built-in documentation

Emacs comes with built-in tutorials and documentation. Moreover, it is a self-documented and self-discoverable editor, capable of introspection to let you know about the current keybindings, to let you search about function documentation, available variables,source code, tutorials, etc. Whenever you ask yourself questions like “what are the available shortcuts to do x” or “what does this keybinding really do”, the answer is most probably a keystroke away, right inside Emacs. You should learn a few keybindings to be able to discover Emacs with Emacs flawlessly.

The help on the topic is here:

The help keybindings start with either C-h or F1. Important ones are:

Some Emacs packages give even more help.

More help and discoverability packages

Sometimes, you start typing a key sequence but you can’t remember it completely. Or, you wonder what other keybindings are related. Comes which-key-mode. This packages will display all possible keybindings starting with the key(s) you just typed.

For example, I know there are useful keybindings under C-x but I don’t remember which ones… I just type C-x, I wait for half a second, and which-key shows all the ones available.

Just try it with C-h too!

See also Helpful, an alternative to the built-in Emacs help that provides much more contextual information.

Built-in tutorial

Emacs ships its own tutorial. You should give it a look to learn the most important keybindings and concepts.

Call it with M-x help-with-tutorial (where M-x is alt-x).


Emacs has, of course, built-in commands to deal with s-expressions.

Forward/Backward/Up/Down movement and selection by s-expressions

Use C-M-f and C-M-b (forward-sexp and backward-sexp) to move in units of s-expressions.

Use C-M-t to swap the first addition sexp and the second one. Put the cursor on the open parens of “(+ x” in defun c and press

Use C-M-@ to highlight an entire sexp. Then press C-M-u to expand the selection “upwards” and C-M-d to move forward down one level of parentheses.

Deleting s-expressions

Use C-M-k (kill-sexp) and C-M-backspace (backward-kill-sexp) (but caution: this keybinding may restart the system on GNU/Linux).

For example, if point is before (progn (I’ll use [] as an indication where the cursor is):

(defun d ()
  (if t
      (+ 3 3)
        (+ 1 1)
        (if t
            (+ 2 2)
            (+ 3 3)))
      (+ 4 4)))

and you press C-M-k, you get:

(defun d ()
  (if t
      (+ 3 3)
      (+ 4 4)))

Indenting s-expressions

Indentation is automatic for Lisp forms.

Pressing TAB will indent incorrectly indented code. For example, put the point at the beginning of the (+ 3 3) form and press TAB:

(+ 3 3))

you correctly get

  (+ 3 3))

Use C-M-q (slime-reindent-defun) to indent the current function definition:

;; Put the cursor on the open parens of "(defun ..."
;; and press "C-M-q" to indent the code:
(defun e ()
"A badly indented function."
(let ((x 20))
(loop for i from 0 to x
do (loop for j from 0 below 10
do (print j))
(if (< i 10)
(let ((z nil) )
(setq z (format t "x=~d" i))
(print z))))))

;; This is the result:

(defun e ()
  "A badly indented function (now correctly indented)."
  (let ((x 20))
    (loop for i from 0 to x
       do (loop for j from 0 below 10
             do (print j))
         (if (< i 10)
             (let ((z nil) )
               (setq z (format t "x=~d" i))
               (print z))))))

You can also select a region and call M-x indent-region.

Open and close parenthesis

When you are in a Slime REPL, you can use C-return or M-return (slime-repl-closing-return) to close the remaining parenthesis and evaluate your input string.

In files, use M-( to insert a pair of parenthesis (()) and the same keybinding with a prefix argument, C-u M-(, to enclose the expression in front of the cursor with a pair of parens.

For example, we start with the cursor before the first paren:

CL-USER> |(- 2 2)

Press C-u M-( to enclose it with parens:

CL-USER> (|(- 2 2))
;; now write anything.
CL-USER> (zerop (- 2 2))

With a numbered prefix argument (C-u 2 M-(), wrap around this number of s-expressions.

Additionnaly, use M-x check-parens to spot malformed s-exps and C-c C-] (slime-close-all-parens-in-sexp) to insert the required number of closing parenthesis.

There are additional packages that can make your use of parens easier:

Hiding/showing code

Use C-x n n (narrow-to-region) and C-x n w to widen back.

See also code folding with external packages.


Insert a comment or comment a region with M-;, adjust text with M-q.

(optional) Packages for structured editing

In addition to the built-in Emacs commands, you have several packages at your disposal that will help to keep the parens and/or the indentation balanced. The list below is somewhat sorted by age of the extension, according to the history of Lisp editing:

We personally advice to try Parinfer and the famous Paredit, then to go up the list. See explanations and even more on Wikemacs.

Search and replace

isearch forward/backward, regexp searches, search/replace

C-s does an incremental search forward (e.g. - as each key is the search string is entered, the source file is searched for the first match. This can make finding specific text much quicker as you only need to type in the unique characters. Repeat searches (using the same search characters) can be done by repeatedly pressing C-s

C-r does an incremental search backward

C-s RET and C-r RET both do conventional string searches (forward and backward respectively)

C-M-s and C-M-r both do regular expression searches (forward and backward respectively)

M-% does a search/replace while C-M-% does a regular expression search/replace

Finding occurrences (occur, grep)

Use M-x grep, rgrep, occur

See also interactive versions with helm-swoop, helm-occur, ag.el.


Emacs Lisp vs Common Lisp

It isn’t necessary to write Emacs Lisp in order to use Emacs with Slime or Sly for Common Lisp.

However learning Emacs Lisp can be useful and is similar (but different) from CL:

Some good Emacs Lisp learning resources:

What about LSP (Language Server Protocol)?

LSP server and client ports for Common Lisp exist, but we don’t need them to have a high quality IDE integration. In fact, Slime/Swank follow a client/server architecture, like LSP, but Slime predates LSP by decades, and still offers much more features for lispers than LSP.

utf-8 encoding

You might want to set this to your init file:

(set-language-environment "UTF-8")
(setenv "LC_CTYPE" "en_US.UTF-8")

and for Sly:

(setf sly-lisp-implementations
      '((sbcl ("/usr/local/bin/sbcl") :coding-system utf-8-unix)

This will avoid getting ascii stream decoding errors when you have non-ascii characters in files you evaluate with SLIME.

Default cut/copy/paste keybindings

I am so used to C-c, C-v and friends to copy and paste text that the default Emacs shortcuts don’t make any sense to me.

Luckily, you have a solution! Install cua-mode and you can continue to use these shortcuts.

;; C-z=Undo, C-c=Copy, C-x=Cut, C-v=Paste (needs cua.el)
(require 'cua) (CUA-mode t)


All Slime REPL shortcuts

Here is the reference of all Slime shortcuts that work in the REPL.

To see them, go in a REPL, type C-h m and go to the Slime REPL map section.

REPL mode defined in ‘slime-repl.el’:
Major mode for interacting with a superior Lisp.
key             binding
---             -------

C-c             Prefix Command
C-j             slime-repl-newline-and-indent
RET             slime-repl-return
C-x             Prefix Command
ESC             Prefix Command
SPC             slime-space
  (that binding is currently shadowed by another mode)
,               slime-handle-repl-shortcut
DEL             backward-delete-char-untabify
<C-return>      slime-repl-closing-return
<C-down>        slime-repl-forward-input
<C-up>          slime-repl-backward-input
<return>        slime-repl-return

C-x C-e         slime-eval-last-expression

C-c C-c         slime-interrupt
C-c C-n         slime-repl-next-prompt
C-c C-o         slime-repl-clear-output
C-c C-p         slime-repl-previous-prompt
C-c C-s         slime-complete-form
C-c C-u         slime-repl-kill-input
C-c C-z         other-window
C-c ESC         Prefix Command
C-c I           slime-repl-inspect

M-RET           slime-repl-closing-return
M-n             slime-repl-next-input
M-p             slime-repl-previous-input
M-r             slime-repl-previous-matching-input
M-s             previous-line

C-c C-z         run-lisp
  (that binding is currently shadowed by another mode)

C-M-x           lisp-eval-defun

C-M-q           indent-sexp

C-M-q           prog-indent-sexp
  (that binding is currently shadowed by another mode)

C-c M-e         macrostep-expand
C-c M-i         slime-fuzzy-complete-symbol
C-c M-o         slime-repl-clear-buffer

All other Slime shortcuts

There is more to what we showed! Slime has shortcuts to disassemble the function definition of the symbol at point, learn how to navigate the inspector, toggle functions profiling, learn its indentation or completion strategies, use multiple Lisp connections, learn how to manipulate presentations

Here are all the default keybindings defined by Slime mode.

To see them, go in a .lisp file, type C-h m and go to the Slime section.

Commands to compile the current buffer’s source file and visually
highlight any resulting compiler notes and warnings:
C-c C-k	- Compile and load the current buffer’s file.
C-c M-k	- Compile (but not load) the current buffer’s file.
C-c C-c	- Compile the top-level form at point.

Commands for visiting compiler notes:
M-n	- Goto the next form with a compiler note.
M-p	- Goto the previous form with a compiler note.
C-c M-c	- Remove compiler-note annotations in buffer.

Finding definitions:
- Edit the definition of the function called at point.
- Pop the definition stack to go back from a definition.

Documentation commands:
C-c C-d C-d	- Describe symbol.
C-c C-d C-a	- Apropos search.
C-c M-d	- Disassemble a function.

Evaluation commands:
C-M-x	- Evaluate top-level from containing point.
C-x C-e	- Evaluate sexp before point.
C-c C-p	- Evaluate sexp before point, pretty-print result.

Full set of commands:
key             binding
---             -------

C-c             Prefix Command
C-x             Prefix Command
ESC             Prefix Command
SPC             slime-space

C-c C-c         slime-compile-defun
C-c C-j         slime-eval-last-expression-in-repl
C-c C-k         slime-compile-and-load-file
C-c C-s         slime-complete-form
C-c C-y         slime-call-defun
C-c ESC         Prefix Command
C-c C-]         slime-close-all-parens-in-sexp
C-c x           slime-export-symbol-at-point
C-c ~           slime-sync-package-and-default-directory

C-M-a           slime-beginning-of-defun
C-M-e           slime-end-of-defun
M-n             slime-next-note
M-p             slime-previous-note

C-M-,           slime-previous-location
C-M-.           slime-next-location

C-c TAB         completion-at-point
C-c RET         slime-expand-1
C-c C-p         slime-pprint-eval-last-expression
C-c C-u         slime-undefine-function
C-c ESC         Prefix Command

C-c C-b         slime-interrupt
C-c C-d         slime-doc-map
C-c C-e         slime-interactive-eval
C-c C-l         slime-load-file
C-c C-r         slime-eval-region
C-c C-t         slime-toggle-fancy-trace
C-c C-v         Prefix Command
C-c C-w         slime-who-map
C-c C-x         Prefix Command
C-c C-z         slime-switch-to-output-buffer
C-c ESC         Prefix Command
C-c :           slime-interactive-eval
C-c <           slime-list-callers
C-c >           slime-list-callees
C-c E           slime-edit-value
C-c I           slime-inspect

C-x C-e         slime-eval-last-expression
C-x 4           Prefix Command
C-x 5           Prefix Command

C-M-x           slime-eval-defun
M-,             slime-pop-find-definition-stack
M-.             slime-edit-definition
M-?             slime-edit-uses
M-_             slime-edit-uses

C-c M-c         slime-remove-notes
C-c M-e         macrostep-expand
C-c M-i         slime-fuzzy-complete-symbol
C-c M-k         slime-compile-file
C-c M-q         slime-reindent-defun

C-c M-m         slime-macroexpand-all

C-c C-v C-d     slime-describe-presentation-at-point
C-c C-v TAB     slime-inspect-presentation-at-point
C-c C-v C-n     slime-next-presentation
C-c C-v C-p     slime-previous-presentation
C-c C-v C-r     slime-copy-presentation-at-point-to-repl
C-c C-v C-w     slime-copy-presentation-at-point-to-kill-ring
C-c C-v ESC     Prefix Command
C-c C-v SPC     slime-mark-presentation
C-c C-v d       slime-describe-presentation-at-point
C-c C-v i       slime-inspect-presentation-at-point
C-c C-v n       slime-next-presentation
C-c C-v p       slime-previous-presentation
C-c C-v r       slime-copy-presentation-at-point-to-repl
C-c C-v w       slime-copy-presentation-at-point-to-kill-ring
C-c C-v C-SPC   slime-mark-presentation

C-c C-w C-a     slime-who-specializes
C-c C-w C-b     slime-who-binds
C-c C-w C-c     slime-who-calls
C-c C-w RET     slime-who-macroexpands
C-c C-w C-r     slime-who-references
C-c C-w C-s     slime-who-sets
C-c C-w C-w     slime-calls-who
C-c C-w a       slime-who-specializes
C-c C-w b       slime-who-binds
C-c C-w c       slime-who-calls
C-c C-w d       slime-who-depends-on
C-c C-w m       slime-who-macroexpands
C-c C-w r       slime-who-references
C-c C-w s       slime-who-sets
C-c C-w w       slime-calls-who

C-c C-d C-a     slime-apropos
C-c C-d C-d     slime-describe-symbol
C-c C-d C-f     slime-describe-function
C-c C-d C-g     common-lisp-hyperspec-glossary-term
C-c C-d C-p     slime-apropos-package
C-c C-d C-z     slime-apropos-all
C-c C-d #       common-lisp-hyperspec-lookup-reader-macro
C-c C-d a       slime-apropos
C-c C-d d       slime-describe-symbol
C-c C-d f       slime-describe-function
C-c C-d g       common-lisp-hyperspec-glossary-term
C-c C-d h       slime-documentation-lookup
C-c C-d p       slime-apropos-package
C-c C-d z       slime-apropos-all
C-c C-d ~       common-lisp-hyperspec-format
C-c C-d C-#     common-lisp-hyperspec-lookup-reader-macro
C-c C-d C-~     common-lisp-hyperspec-format

C-c C-x c       slime-list-connections
C-c C-x n       slime-next-connection
C-c C-x p       slime-prev-connection
C-c C-x t       slime-list-threads

C-c M-d         slime-disassemble-symbol
C-c M-p         slime-repl-set-package

C-x 5 .         slime-edit-definition-other-frame

C-x 4 .         slime-edit-definition-other-window

C-c C-v M-o     slime-clear-presentations

See also

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